Electromagnetic recorder wire and method of making it



Patented Dec. 18, i951 UNITED STATE S PATENT-,LCFFICE. 2,578,782 Y ELECTROMAGNETIC RECORDER WIRE ND METHOD OF MAKING IT Charles H. Campbell, Bedford; Ronald E; Grit fiths, Cleveland Heights, and Willis T. Cranier, Rocky River, Ohio, assignors to The American Steeland Wire Company of NewJersey, a 001! poration of New Jersey No Drawing. Application November 4,1948, 9 Serial No. 58,362 V i 3 Claims. (01. 148-342),

limit the space needed to accommodate the 7 length necessary for -a, given'period ,of recording. It must also have high tensile strength to insure agamst breakage while recording or reproducing.

Magnetically, the wire should have a residual induction sufiicient to preserve a record against the tendency to self-demagnetization,and a coercive force high enough to aid preservation but low enough to permit complete erasure of a record when desired. The volume of noise or random sounds emitted when running through the re-' producer a wire without-any signal recorded thereon, must be considerably'below the volume ofsound produced by a normal recorded signal.

Finally, a high degree of uniformity in magnetic characteristics is necessary throughout the length of the wire.

Stainless-steel wirehas been employed for recording purposes because of its corrosion re-, sistance, among other reasons, which is highly desirable in wire as fine as .004", despite the fact that stainless steel isnormally austenitic and therefore non-magnetic. The austenite is metastable, however, and is decomposed to a ferrite aggregate on cold-working as by drawing through reducing dies. a method of processing stainless-steel wire by which we are able to control this decomposition of austenlte and thus produce material having improved properties for, use as a recording medium. .In particular, the product of our method satisfies the requirements of recorder manufacturers for a ,high-fidelity medium of uniform characteristics, exhibiting a. wide range of frequency response and an acceptably low noise level. These requirements have naturally become more exacting with the progress of the magnetic recording art. At present, some manufacturers prefer recorder wire having a coercive force (He) between 160 and 450 oersteds and preferably between 225 and 325 and a residual induction (Br) between 1500 and 6000 gausses and preferably between 2500 and 3000, although higher values are desired by certain users. We have discovered that thesecharacteristics are affected to'varying degrees by the several factors involved in the. processing, i. e., the annealing tempera- We have discovered ture,-the extent and rate of cold reduction'and the temperature at which it is conducted-aswell as by the compbsitionof the metal and, by our invention, we are able to correlate these factors. in'such manner as to produce recording wire having the desired qualities to a degree not attained hitherto.

Generally speaking, our method consists in an- --nealing hard-drawn stainless-steel Wire of the composition hereinafter disclosed and a diameter several times the desired finished diameter, at a temperature considerably below that at which such steels have. customarily been annealed,

thereby austem'tizing the steel, and drawing the wire down to the desired final size with a heavy reduction, i. e., over 70%. We find that this practice will decompose the austenite sufiiciently "'to' precipitate enough ferrite to impart the desired'magnetic properties to the product. We

correlate the extent to which the steel is austenitizedwith the amount of, cold work performed in drawing the wire to final size.-

111m apreferred practice of our invention, we

start with a heat of stainless steel preferably composed of from 8 to 12% nickel, from 17 to 20% chromium, from 0.6 to 12%;carbon, and the balance substantiallyiron,except for the usual amountsof impurities}. e Mn 2% max '1 and". S -.02% and .Si .75 max. The analysis which seems togive .best results is about 10.5% nickel, about-l8% chromium and .09 or 10% carbon. The steelis processed by hot-rolling to the form of wire rod and the rod is drawn downprogrs sively to a diameter of about .040", with intermediate annealing as necessary in accordance with usual practice. After annealing at a, diameter of about .040", the wire is further drawn downto a' diameter of -.020 or less, say about; .012, or even as small as .008", From this point on, we controlv the subsequent processing in a particular manner to be described in detail, in order to produce recorder wirehaving the desired characteristics; I

The. first step inthe final stage of processing.

according to our invention is a continuous annealing of the wire .002 or less in diameter, at a temperature of from 1500 F. to 1850 F. and: preferably about 1700" F. In making stainless steelwire, ithas. always been the practice .herea; tofore: to anneal at a higher temperaturesuchas .2150? F. but wefind that. annealing in the lower range of temperatures specified gives a2 final product having the desired coercive force'i and lowjnoise level. Annealing above 185091.

results "in, material having an excessive noise,

level and, generally speaking, the lower the annealing temperature, the lower is the noise level. Annealing at a temperature in the lower part of the range given,' say between 1500 and 1700 F., raises the residual induction for a given coercive force. The trend of recorder manufacturers is toward higher residual inductions, so high in fact that amplification may bereducedor even eliminated in some cases.

on the characteristics of the product. Ordinarily in drawing stainless steel wire to a size of .004 the temperature of the liquid lubricant with which the dies are flooded will run but little r1 higher than room temperature. In contrast to this, we maintain the lubricant at a temperatime above room temperature and in some cases considerably above it. The temperature should be between 115 and 135 F. for steel having a As the annealing temperature of the hard 10 nickel content in the upper portion of the range,

drawn wire is decreased from about 1800 'F., there occurs, in increasing. amounts, a fine precipitation of chromium iron carbide. This removal of both chromium and carbon from ausi. e.,'from to 12%. For lower nickel content, 7 the lubricant temperature should be higher, say 135 to 190 F. The more extreme the reduction after final annealing, the higher the lubritenite decreases the stability of the alloy thus 15 cant temperature should be, unless the analysis making it possible to adjust thecoercive force and residual induction by utilizing an economical heavy final reduction. Annealing within lower J part of the temperature range also improves the is such that more cold work is needed to prec'ipitate out the amount of ferrite required to give the desired magnetic properties. The lower the lubricant temperature, the higher the residnoise characteristics and residual induction of ual induction and the lower the coercive force.

the wire and decreases the austenite stability as compared with that annealed at the higher temperatures. This is probably due to the small The following table gives in compact form the details of several typical examples of our method and the results obtained thereby:

No. Drafts steds ses Anneal From To Per Cent (Heat 3422, analysis: 0, .10% Mn, 1.14%; P, .0l1%; S, .012%; Si, 37%; Cr, 17.58%;

(Heat 3166, analysis: 0, 06%; M11, 1.16%; P, 020%; S, .008%; Si, Cr, 17.26%; N1, 11.84%.)

(Heat 6559, analysis: 6, .10%; Mn, 54%; P, 017%; S, 010%; Si, .57%; Or, 19.25%;

1, 700 00s 004 75 s 250 2, 375 1, 700 009 004 so 7 260 3, 000 1, 700 0075 004 71 l 5 240 2, 000

grain size and fine precipitation of carbides affecting the magnetic domain size within the wire. Wire annealed at-these low temperatures gives somewhat higher residual inductions than that obtained from *material annealed at the 5 The addition of from 2 to 3% molybdenum to steels of the above types will produce a wire having a higher residual "induction and approximately the same coercive force.

It will be apparent from the foregoing that our invention makes it possible to produce 'recorder wire having characteristics within the optimum ranges which have been set up as specifications by recorder manufacturers. Our meth- 55 0d, furthermore, may be performed without a material increase inthe cost compared to prior practice and the technique involved may be easily applied in existing wire-drawing plants.

Although we have described only a preferred which the drawing is conduc e particularly practice andcertai'n modifications, it willbe unimportant. The number of reduction steps or drafts taken, for example, varies the coercive force and residual induction. For a reduction such as that contemplated, from 10 to 17 drafts will ordinarily be required. The greater the 5 number of drafts for a given reduction, the lower the coercive force and the higher the residual induction. The number of drafts also varies with the'nickel content of the steel. For example,

derstood that changes in the procedure disclosed may be made within the scope of the following claims.

We claim:

1. In a method of making wire suitable for electro-magnetic recording, the steps including hot-rolling steel containing from 8 to 12% nickel, 1'7 to 20% chromium, from .06 to .12% carbon and the remainder substantially iron, to the form steel containing 10% nickel or more should be f a rod, alternately annealing and colddmw;

reduced in from 15 to 17 drafts. Steel containing 8.5% nickel may be reduced in from 10 to 14; drafts.

'-We find that the temperature at which the ing the rod in aplurality of steps to a wire having a substantially meta-stable austenitic structure and a diameter between .020" and .008", annealing the resulting wire at a temperature of drawing is carried on has a pronounced effect from 1500 F. to 1850F., effecting'a total reduction in the sectional area of the wire of at least 70% by cold-drawing the wire in from ten to seventeen drafts, maintaining the Wire during the last-mentioned cold-drawing in a medium at a temperature between 115 and 190 F., and finishing at a diameter of .006" to .003" thereby producing wire having a fine precipitation of chromium-iron carbide and ferrite dispersed throughout its austenitic matrix, and having in its finished state a coercive force between 160 and 450 oersteds and a residual induction between 1500 and 6000 gausses.

2. Recorder wire from .006 to .003" in diameter composed of steel containing from 8 to 12% nickel, from 17 to 20% chromium, from .06 to 12% carbon and substantially the balance iron, and having an austenitic structure with a fine precipitation of chromium-iron carbide and ferrite dispersed throughout its austenitic matrix and having a coercive force between 160 and 450 oersteds, a residual induction between 1500 and 6000 gausses and the other characteristics of wire produced by hot-rolling steel of the composition specified to the form of a rod, alternately annealing and cold-drawing the rod in a plurality of drafts to a wire having a substantially meta-stable austenitic structure and a diameter between .020" and .008, annealing the resulting wire at a temperature of from 1500 F. to 1850 F., effecting a total reduction in the sectional area of the wire of at least 70% by colddrawing the wire in from ten to seventeen drafts, maintaining the wire during the last-mentioned cold-drawing in a medium at a temperature between 115 and 190 F.

3. In a method of making Wire suitable for electro-magnetic recording, the steps including providing wire several times the desired finished diameter composed of steel containing from 8% to 12% nickel, 17% to 20% chromium, from .06 to .12% carbon and the balance substantially iron, annealing the wire at a temperature between 1500 and 1850 F., effecting a total reduction of at least in the sectional area of the wire to a size of about .004" in diameter by colddrawing the wire through from ten to fourteen reducing dies when the nickel content of said steel is in the lower part of its range and by cold-drawing the Wire through from fifteen to seventeen dies when the nickel content of said steel is in the upper part of its range.-

CHARLES H. CAMPBELL.v RONALD E. GRIFFITHS. WILLIS T. CRAMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES The Book of Stainless Steels, Thum, pages 117-119. Published by Amer. Soc. for Metals, Cleveland, Ohio, 1935.

Transactions of the A. S. S. T., vol, 20, pages 104-106. Published by Amer. Soc. for Metals, Cleveland, Ohio, 1932. 

